This invention relates to a process for the production of core rolls for the winding of sheet materials, and more particularly for the roll up of base papers for photographic layers.
In general such winding core rolls are formed of paper or cardboard, as well as plastic, metal or wood. The following requirements are placed on core rolls for the rolling up of sheet materials like papers or foils:
The core roll should not sag as the result of the weight of the sheet materials. PA1 The cross-section of the core roll should not deform during the roll up or roll off process. PA1 The core roll should have a definite moistness and, if applicable, contain a moisture barrier of metal to prevent the exchange of moisture between the core and the paper. PA1 The core roll should be abrasion proof, that is the surface of the core roll should not be damaged upon fixing the sheet material to it with an adhesive band or the subsequent removal of the band. PA1 The surface of the core roll should be uniform and have no markings. PA1 The core roll should only be subject to static charges to a limited extent to avoid undesirable contamination of the sheet material by dust particles which are attracted by the core roll. PA1 In the event that the sheet material is a photographic base paper, the coating of the core roll should be photochemically compatible.
A high radial pressure prevails within the core roll due to a certain intensity of winding. This pressure leads to the pressing of irregularities onto the sheet of material which is to be rolled on the core roll, such as the edge of the sheet, as well as by the adhesive band which is used for the fixing of the sheet. As the result, clearly visible and undesirable markings occur which are visible on the last 20 to 40 meters of the paper sheet. This material is considered to be waste material.
Attempts have been made to counteract the problem of the impressions and markings through the production of specially hard, smooth core rolls. As the result, the markings which occur due to the irregularities in the core roll surface are avoidable. However, the markings which arise due to the edge of the sheet and the fixing of the sheet can not be avoided.
One other attempt to solve this problem is described in German DE-OS 36 10 557. It discloses core rolls which are coated with a deformable, primarily foamed material. The undesirable markings and the resulting waste can be reduced by that means to approximately 5 to 10 meters. A disadvantage of these core rolls is that they can only be disposed of with difficulty and their manufacture is more expensive because of their compound character.
The materials which have been used up to this point for the coating of the core rolls in the form of a tube, band or foil, are fixed with the help of an adhesive to the surface of the core roll. In the alternative they can be applied by extrusion or foaming. This type of coating and its fixation to the surface of the core roll is expensive and makes the disposal of the core rolls more difficult.
German patent DE-PS 644 166 describes the drawing or positioning of elastic tubes by means of suction or pressure on the rolls. In accordance with one form of implementation, the elastic tube is drawn onto the roll a short distance by hand, and on the other end it is sealed through drawing by hand onto a mouthpiece which is connected with a compressed air pump. The tube is then pumped up and drawn in the pumped up condition over the roll. The presupposition for this procedure is a certain inherent stability, that is to say, a certain thickness of the tube, because damage can otherwise occur. In accordance with a second implementation, an underpressure is produced between a hollow body and the elastic tube which is introduced into it, and the latter is consequently held by suction to the internal wall of a mounting pipe. The widening and fixing of the tube by means of underpressure requires a high expenditure in sealing between the tube and the mounting pipe. Moreover, there is a disadvantage that the object which is to be drawn over can now no longer be inserted into the hollow body in a sliding manner on an air cushion. Any abutting of the roll on the rubber tube can lead to damage, so this procedure cannot be recommended.
In accordance with German DE-PS 645 917, a tube which is outside of a hollow body, but which is attached to it, is inflated, and the object which is to be covered with the tube is inserted into the expanded tube. The disadvantage in this procedure is that the tube is not fixed in the hollow body. Like the implementations described above, this procedure can only be carried out with tubes that have a certain wall thickness.
It is thus the task of the present invention to provide a process for the production of core rolls for the rolling up of sheet materials in which the core rolls cause no undesirable markings on the sheet materials. Thus, the usual waste is reduced to a minimum and the product can be produced in a manner free of problems. The process of the invention is particularly well suited for the rolling up of base papers for photographic layers.
A rubber tube is applied against the internal wall of a mounting pipe by inflation with compressed air or a similar pressure agent at a pressure of about 0.2 to 0.5 bar. The mounting pipe with the rubber tube is then slid onto the core casing and, after the pressure is reduced, it is applied tightly against the core casing, whereby the rubber tube is held in an unmovable manner by a pressure which is exerted by the rubber tube against the surface of the core casing. After the application of the rubber tube, the projecting ends of the tube are cut off, preferably with a heated blade, and the edges are consequently protected against tears.
The core casing which is used for the production of the core rolls in accordance with the invention is preferably a paperboard casing, the surface of which can be unprocessed.
The ratio of the internal diameter of the rubber tube to the external diameter of the core casing is preferably about 0.70:1 to 0.95:1. The thickness of the rubber tube may vary in range from about 0.5 to 5 mm, and preferably 1 to 3 mm. The material of the rubber tube is a rubber with a hardness of from about 20 to 50 shore, and preferably 30 to 45 shore. In one special embodiment of the invention, the rubber material is an acid resistant rubber which contains a softening agent.
Surprisingly, the core rolls which are produced in accordance with the present invention have been found to reduce the accumulation of material waste, which at the present time is approximately 40 meters per roll in the case of paper, to less than 5 meters. In addition to the waste reduction, this small amount of waste has the advantage that it may be left on the core roll and its quantity is sufficient to protect the rubber surface of the core roll and provides security in transport. After the core roll has been freed of the remaining small amount of paper waste and cleaned, it can be used again. Moreover, the paperboard casing which is used as a core casing does not require any moisture barrier of folded aluminum foil. In view of this it can be recycled free of any problems.
Because the rubber coating tube only adheres to the surface of the core casing by its residual stress, no compound material is brought about. In the event of a defect in the casing, the rubber tube can be separated from the core casing in the simplest manner, for example by a blade cut, and both materials can be recycled again as work materials.
The adhesive band which is used for fixing of the edge of the paper sheet to the core roll can be removed from the rubber surface without any surface damage to the core roll.